Branch Circuit Monitor

ABSTRACT

A branch circuit monitoring system (BCMS) for monitoring branch circuit currents in one or more electrical circuit panels is described. The system is comprised of a data center server, one or more panel processors, each with one or more collection devices, and one or more current sensors per collection device. The BCMS is designed to be installed entirely inside the panel without the need for a dedicated enclosure or power supply to facilitate ease of installation and low-cost. The BCMS also allows for future upgradability through standard software updates so that the system can be updated or patched easily. The BCMS data center server collects, aggregates, stores, and serves historical branch circuit current data from the panel processors to networked users via a web server to provide visualization of data such as tables, charts, and gauges. Finally, the BCMS interfaces to third-party software suites using industry-standard protocols such as Modbus® TCP and BACnet™ for integration with data center infrastructure management or building management system software.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/108,134 entitled “Branch Circuit Monitor” filed by Montgomery J.Sykora et al. on Dec. 16, 2013, which is a continuation of U.S. patentapplication Ser. No. 13/963,844 entitled “Branch Circuit Monitor” filedby Montgomery J. Sykora et al. on Aug. 9, 2013, each of which is herebyincorporated by reference as though fully set forth herein.

This application is a continuation of This application claims thebenefit of U.S. provisional application No. 61/681,406 entitled“Apparatus, System and Method for Branch Circuit Monitoring” filed byMontgomery J. Sykora on Aug. 9, 2012 and U.S. provisional applicationNo. 61/681,527 entitled “Apparatus, System and Method for Branch Circuitand HVAC Monitoring and Control for Optimal Cooling and EnergyEfficiency” also filed by Montgomery J. Sykora et al. on Aug. 9, 2012,both applications are hereby incorporated by reference as though fullyset forth herein.

BACKGROUND

1. Field

Aspects of the present disclosure involve a branch circuit monitoringsystem providing information concerning the utilization of individualbranch circuits, particularly within a data center, and providing theability to manage those circuits so that individual circuits are notoverloaded while at the same time fully utilizing various circuits.

2. Background

Branch circuit monitoring (BCM) devices typically utilize a multitude ofcurrent transformers (CTs) connected to a sampling and processing board,either directly or via an intermediary circuit board. The CTs generate avoltage or current electric signal that is proportional to the currentflowing in the branch circuit. The standard procedure dictates asampling of the electric signal and performing mathematical calculationsto determine the RMS current. Additional calculations such as realpower, apparent power, power factor, and kWh are possible with theestimation or measurement of the voltage of the branch circuit. However,because the circuits are limited by the circuit breaker current rating,the most important and useful measurement is the RMS current value. Thisvalue is used to determine if a circuit is in danger of beingoverloaded, or can be summed with other current values to give a phasecurrent total. Some BCM devices use digital signal processors and amultitude of analog-to-digital (A/D) converters to accomplish this. Asthe number of circuits monitored grows, the size and complexity of thecollection and processing circuitry increases, leading to large systemsand relatively high prices per panel. A typical data center may havehundreds of panels and thousands of circuits to monitor, makingconventional BCM devices prohibitively expensive to install.

Typical BCM devices require that the circuit panel be de-energized topass the circuit wires through the CTs, making retrofits difficult indata centers that need continuous operation (or up-time). Use ofsplit-core CTs alleviates some of the difficulty of installing a BCM ina “live” panel, but in general, the main processing circuitry still hasthe disadvantage of being large and requiring a separate cabinet andpower supply for installation. These two requirements increase the costand complexity of the BCM device installation.

In addition, most prior art BCM devices are designed withapplication-specific processors and circuitry. This makes upgrading orimproving the system difficult and expensive, if even possible.

BRIEF SUMMARY

In accordance with one embodiment a branch circuit monitoring (BCM)device comprises a programmable panel processor, a plurality of small,modular collection devices, and a plurality of non-contact currentsensors.

Accordingly several disadvantages described above can be alleviated ormitigated by the apparatus, system and methods described herein alongwith additional desirable features.

An improved branch circuit monitoring device, system and methods aredescribed herein. The device, system and methods overcome the majorissues with current BCM devices and systems: high cost, installationcomplexity, and obsolescence. These factors are interrelated and areaddressed by multiple approaches and methods. Together, the features andimprovements presented make branch circuit current monitoring affordableand feasible for existing data centers.

The complexity of the BCM device is reduced while simultaneouslydecreasing the size and footprint of the apparatus to allow a low-costsystem to be installed easily inside a standard panel board withoutexternal enclosures or a dedicated power supply. The use of accurateRMS-to-DC voltage converter circuitry on small, decentralized collectionboards allows for relatively inexpensive general purpose processor to beutilized for the data aggregation and processing while maintaininghighly accurate current values. Finally, standard networking protocolssuch as TCP, HTTP, UDP, as well as any specific protocols such asBACnet™, Modbus®, or SNMP are supported. The system supports long-termdata storage, retrieval, and visualization using modern, open-sourceprograms and methods and the ability to integrate numerous BCM devicesinto a system.

In one implementation, a branch circuit monitoring system is providedcomprising: a first plurality of current sensors each coupled with atleast one branch circuit of a first plurality of branch circuits, eachrespective current sensors of the first plurality of current sensorsconfigured to measure a current within one of the respective firstplurality of branch circuits and to provide a signal indicative of themeasured current value; a first collection device configured to receivethe signals indicative of the measured current value from each of thefirst plurality of current sensors and convert the signals indicative ofthe measured current value from each of the first plurality of currentsensors from an alternating current (AC) signal to a direct current (DC)signal; a second plurality of current sensors each coupled with at leastone branch circuit of a second plurality of branch circuits, eachrespective current sensor of the second plurality of current sensorsconfigured to measure a current within one of the respective secondplurality of branch circuits and to provide a signal indicative of themeasured current value; a second collection device configured to receivethe signals indicative of the measured current value from each of thesecond plurality of current sensors and convert the signals indicativeof the measured current value from each of the plurality of currentsensors from an alternating current (AC) signal to a direct current (DC)signal; and a panel processor in communication with the first and secondcollection devices configured to receive the first and second pluralityof DC signals, the panel processor configured to store in a local memorya plurality of data structures comprising the measured branch circuitcurrent data values for said branch circuit along with a timestampassociated with a time at which the currents were measured.

In another implementation, a method of monitoring branch circuits isprovided comprising: measuring a first plurality of currents within afirst plurality of branch circuits using a first plurality of currentsensors each coupled with a respective branch of the first plurality ofbranch circuits; receiving, at a first collection device, a firstplurality of signals indicative of the first plurality of measuredcurrent values of the first plurality of branch circuits; converting, atthe first collection device, the signals indicative of the measuredcurrent value from each of the first plurality of current sensors froman alternating current (AC) signal to a direct current (DC) signal;measuring a second plurality of currents within a second plurality ofbranch circuits using a second plurality of current sensors each coupledwith a respective branch of the second plurality of branch circuits;receiving, at a second collection device, a second plurality of signalsindicative of the second plurality of measured current values of thesecond plurality of branch circuits; converting, at the secondcollection device, the signals indicative of the measured current valuefrom each of the second plurality of current sensors from an alternatingcurrent (AC) signal to a direct current (DC) signal; receiving, at apanel processor in communication with the first and second collectiondevices, the first and second plurality of DC signals; and storing, in alocal memory of the panel processor, a plurality of data structurescomprising the measured branch circuit current data values for saidbranch circuit along with a timestamp associated with a time at whichthe currents were measured.

The foregoing and other aspects, features, details, utilities, andadvantages of the present invention will be apparent from reading thefollowing description and claims, and from reviewing the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example implementation of a branch circuit monitoringsystem.

FIG. 2 shows an example implementation of a collection device that maybe used within a branch circuit monitoring system such as shown in FIG.1.

FIG. 3 shows example implementation of a panel processor coupled to aplurality of collection devices.

FIG. 4 is a view of an example BCM device installed in a circuit panelboard.

FIG. 5A shows an example collection device circuit board, also known asa CT interface (CTIF) board.

FIG. 5B shows a simplified schematic of an example analog processingchain on the CTIF board.

FIG. 6 shows the BCM device from software and networking perspectives.

FIG. 7 shows the BCM System (BCMS) block diagram.

FIG. 8 shows the alternate embodiment of the CTIF board with Hall Effectsensors.

FIG. 9A depicts a calibration setup.

FIG. 9B gives an example algorithm flowchart to accomplish thecalibration for a sensor.

DETAILED DESCRIPTION

Modern data centers host a tremendous number of computing devices, suchas web servers and the data storage systems necessary for enterprisesoftware operations, cloud computing, Internet access and applications,and numerous other computing functions. The power for the physicalequipment within the data center is supplied by branch circuits. So, forexample, a rack of servers that are used to host a website may besupplied by a single 20 Amp rated branch circuit. These branch circuits,as illustrated in FIG. 1, originate from a power panel where the sourceof power is received, which may be a 120 volt, 208 volt or otheralternating current (AC) supply, and which may be two or three phase.The power supplied to the panel is then distributed across some numberof discrete branch circuits. Conventional panels may include 42 or 72branch circuits with each circuit also including a breaker.

FIG. 1 shows one example implementation of a branch circuit monitoringdevice 10. A branch circuit monitor 10 is a device that enables themonitoring of individual branch circuits 12 of an electrical panel 14. Atypical panel contains 42 or 72 branch circuits, although other panelconfigurations are possible. These circuits are then routed to equipmentor equipment racks where individual computers, networking devices, orsimilar components draw power from one or more circuits. The monitoringof the branch circuit current values can be used, for example, totrigger alarms, both locally and remotely, as well as be archived in adatabase for retrieval and analysis.

In one example, the branch current monitor 10 is configured to measureand log the branch current of a plurality of branches spanning the powerpanels of the data center. One or more current sensors 16 are used tomonitor the current of each branch circuit 12. In some cases, more thanone current sensor 16 may be deployed across various sub-branches of abranch circuit 12. The sub-branch currents may later be summed, such asby a management board, to determine a total branch current.

In one implementation, each of the current sensors 16 (e.g., currenttransformers (CTs)) connects to a collection device 18 (e.g., a currentmeasurement board or other collection device) located in the power panel14. The current sensors 16 provide the collection device 18 with asignal indicative of the branch circuit current. The collection device18 uses the signal from the current sensor 16 to produce a voltage (orother signal) indicative of the measured current that can be understoodby a panel processor 20. The panel processor 20 receives each voltagesignal (or other type of signal), calculates a current, and stores thecurrent measurement along with a timestamp and address in a memory 22.This information may be later relayed to a server, such as the DataCenter BCM Server 24 shown in FIG. 1, for longer term storage in adatabase, such as BCM Database 26 shown in FIG. 1. The server 24 mayperiodically report measurements to a building management system (BMS)28 and/or to a user. Users may also alter the configuration of thebranch current monitor 10 by accessing the server 24. A user interface30, such as a display with a graphical user interface (GUI), may be usedto report data or other information to a user.

FIG. 2 shows an example implementation of a collection device 40 (inthis implementation, a current measurement board although othercollection devices are contemplated) that may be used within a branchcircuit monitoring system, such as the branch circuit monitor 10 shownin FIG. 1. In this particular implementation, the collection device mayutilize any method form measuring current and provide the currentmeasurement to a panel processor 50 (shown in FIG. 3). As shown in FIG.2, the collection device 40 may include a rectifier/signal conditioningelement 42, an analog-to-digital (A/D) converter 44, and an outputconnection 46. Together these elements may be configured to convert thesignal captured by the current sensor 48, such as a CT, into a signalthat is usable by the panel processor 50. For example, therectifier/signal conditioning element 42 may comprise a resistor coupledto a voltage rectifier to convert the AC resistor voltage to anequivalent direct current (DC) voltage. The resistor may be connected tothe terminals of the current sensor 38 (e.g., CT). When branch circuitcurrent is nonzero, a current will flow through the resistor creating ameasurable voltage drop. If the branch circuit has an AC voltage, theresistor voltage will likewise be an AC voltage. In many cases, it maybe beneficial to convert the AC resistor voltage to an equivalent DCvoltage using the rectifier of the rectifier/signal conditioning element42. This element may also comprise a signal conditioner configured toprepare the signal for use by the A/D converter 44. The signal may beamplified (or scaled down) to be in an operable range of the A/Dconverter 44 and may also be filtered to remove excess noise. Forexample, the A/D converter 44 may be configured to accept a DC input andthe rectifier may only provide a 0 to 1V output. In this case, it may bebeneficial to amplify the output of the rectifier in the signalconditioner 42 to produce an output signal. The rectified andconditioned signal is then communicated to the A/D converter 44 whichthen converts the signals from each current sensor 48 into digitalvalues and produces an output for transmission to the panel processor50. The A/D converter 44 interfaces with a connection element 46, suchas a standard RJ45 connection or any other suitable electricalconnection. In one example, the connection element 46 may also beconfigured to receive DC power from the panel processor 50.

In one specific implementation, each collection device is connected withor otherwise configured to receive an input from N current sensors 48(e.g., 1 to 8 current sensors). Depending on the implementation,however, any number of current sensors may be connected with to acollection device. Likewise, each power panel may have a singlecollection device or a plurality of collection devices depending on thenumber of branch circuits and the implementation of the collectiondevices.

FIG. 3 shows an example implementation of a panel processor 50 coupledto a plurality of individual collection devices 40, such as thecollection device 40 shown in FIG. 2. In one example, the panelprocessor 50 may comprise an input circuit 52, a processor 54, a datastorage element such as a memory 56, and a network connection 58. Theprocessor 54 is configured to perform current calculations by executinginstructions stored in the memory 56. The memory 56 may also store anyneeded constant values for current calculations. Once each currentcalculation is completed, the processor 54 may store the results in thememory 56 along with an address associated with the result, and atimestamp. The network connection 58 may then be used to send thecurrent measurement(s), the address(es), and a timestamp(s) to a server60 at regular intervals, irregular intervals, or based on a command fromthe server 60. Furthermore, the panel processor 50 may receiveconfiguration data from the user via the server 60.

A branch circuit monitoring server 60 is coupled with each panelprocessor within a data center. Since there may be hundreds of panels ina data center, there may in turn be hundreds of panel processorsobtaining and recording data from thousands of branch circuits. Theserver 60 is connected with a database (see, e.g., FIG. 1) and isconfigured to request data from the processors 54 of the panelprocessors 50 and store the collected data in the database (or otherform of data storage). Like the processor 54, the database may includethe branch ID, the current value and the time stamp. Once the data iscollected from the processors 54 of the panel processors 50, the memory56 at the panel processors 50 may be cleared thereby allowing the memorysize at the panel processors 50 to be relatively small. Similarly, thecollection device may have only sufficient memory to store only the mostrecent measurements or some number of measurements that would occurbetween polling cycles of the panel processor to the collection device.

The server 60, panel processors 50 and collection devices 40 arearranged in a programmable modular system. Thus, the system may bedeployed in any data center with any number of branch circuits; thesystem easily adapts to the addition or removal of circuits, and doesnot require extensive customization for deployment. Moreover, the server60 and panel processors 50 may be configured for self-discovery of newcollection devices, circuits, etc., so that user programming orconfiguration of the system is minimized or even eliminated. A buildingmanagement system may be configured to receive and display the measuredparameters. In one example, the building management system is connectedto the server by way of a Modbus® TCP connection, although other formsof standard or proprietary communications protocols are possible.

Besides the ability to view the data, the system also provides the datacenter or the purchasers of a circuit to manage the circuit usage. Inone example, the data center may utilize the full capacity of a givencircuit or set of circuits before installing additional panels andcircuits. If, for example, a 20 amp circuit is a supplying at most 10amps, then there are approximately 8 amps of underutilized capacity onthat circuit (considering that it is typical practice to not fully loadthe circuit in order to avoid tripping the breaker). Across severalpanels there may additional underutilized capacity. Thus, the circuitsmay be rearranged or additional equipment coupled with the circuitrather than adding additional panels. Similarly, if a circuit is runningover its maximum rated capacity, say consistently at or near 20 amps,then some load can be removed from the circuit and thereby avoid downtime for the equipment coupled with the circuit when the breaker trips.The BMS module within the BMS system may be further configured toautomatically notify the user when such conditions occur.

In this implementation, the panel processor 50 is connected with andconfigured to collect data, such as via polling or interrupt, from thecollection devices 40 (e.g., a plurality of individual currentmeasurement boards). In one specific implementation, for example, eachof the collection devices 40 is connected with the panel processor 50 byway of a twisted pair parallel connection, although other forms ofcommunication and connection are possible, such as I2C, SPI, or USB. Asdiscussed above, the panel processor 50 includes an input 52 forreceiving the data from the collection devices 40, a processor 54, and astorage device, such as some form of memory 56, where the data is storedat the panel processor 50. In one example, the processor 54 stores anindication of the branch where a particular measurement was taken (e.g.,a branch ID), the measured current, and a time stamp.

In one implementation, each collection device is connected with orotherwise configured to receive input from eight current sensors.Depending on the implementation, however, any number of branch circuitsmay be connected with a collection device. In one implementation, thecollection device is configured to poll each branch circuit monitor onceper second or at some other interval or in response to a command, andmay further be configured to store the measured current with associationto the branch circuit where the measurement was taken as well as thetime.

The panel processor 50 receives the measurements from each of thecurrent sensors via the collection devices 40. Thus the panel processor50 receives one or more DC voltage inputs from each collection device40. In this implementation, the panel processor 50 is adapted to receivea very large number of signals as the system is expanded to cover moreand more branch circuits. For example, the panel processor 50 may haveone input for every current sensor. To handle these inputs, the panelprocessor 50 may employ an input circuit 52 comprising multiplexers andlogic circuitry as needed. Furthermore, additional panel processors 50may be added once a panel processor 50 has run out of inputs.

Once receiving the current measurements, the panel processor 50 may thenconvert the voltage measurements into current readings constantly,according to a schedule, or according to a user command. Using theexample provided above, the panel processor 50 may constantly receive a0 to 5 VDC signal representing a voltage drop across a resistor. Thepanel processor 50 may then solve for the branch current by determiningthe resistor current (using Ohm's law and accounting for any gainproduced by the output circuit) and compensating for the turns ratio ofthe CT.

One particular implementation of a BCM device 100 is illustrated in FIG.4. In this particular implementation, the BCM device 100 comprises apanel processor 101, one or more collection devices 102 (e.g., currentmeasurement or collection circuit boards), and one or more currentsensors 103 (e.g., current transformers (CTs)) per collection device.The panel processor 101 may comprise any known processor, such as ageneral purpose processor, a special purpose processor, an ASIC, adigital signal processor (DSP) or the like. In the particularimplementation of FIG. 3, for example, the panel processor comprises anARM Cortex-8 processor using a Linux operating system with an easilymodifiable programming language to ensure upgrades, patches, andadditional features are as simple as upgrading a standard PC computer.In an alternate implementation, other processors and operating systemssuch as an Intel Atom processor using Windows 8 RT can be used. In oneimplementation, the BCM device uses split-core CT current sensors oneach circuit to allow for easy installation of “live” panels without theneed to de-energize.

Implementations of the BCM device may also use solid core CTs, or othercurrent sensors such as Hall Effect sensors, or Rogowski coils. In oneparticular implementation, the panel processor, collection boards, andcurrent sensors are small modular devices that are adapted to beinstalled inside of the panel enclosure. In this implementation, thecollection devices connect to the panel process by means of amulti-conductor cable, such as a category 5 (Cat 5) Ethernet cable 104for a simple parallel transmission of control and sensor signals orribbon cable for a serial connection of the collection devices in adaisy-chain fashion in an alternate embodiment. The current sensorsconnect to the collection devices by means of a simple twisted paircable 105. The only external connection to the BCM device, in thisimplementation, is a power-over-Ethernet cable (PoE) 106 that interfacesto a commercial-off-the-shelf (COTS) PoE splitter 107. The PoE splitter107 passes network communications to and from the panel processorEthernet interface and the rest of the network, and also provides 5V DCpower to the panel processor.

FIGS. 5A and 5B show physical and logical depictions of an exampleimplementation of a collection device and its corresponding currentsensors. In this particular implementation, for example, the currentsensors comprise current transformer (CT) current sensors 203 and thecollection device comprises a current transformer interface (CTIF) board202. The CT current sensors 203 are coupled to each branch circuit andprovide a signal indicative of the current flowing through the branchcircuit to the CTIF board collection devices 202. In the case of the useof a CT current sensor 203, as shown in FIGS. 5A and 5B, the CT currentsensor 203 may be both physically and inductively coupled to a componentin the branch circuit, such as a power cable, a circuit breaker, or anyother component that has the full or partial branch current. The CTcurrent sensor 203 is also connected directly to the CTIF boardcollection device 202, providing the CTIF board collection device 202with a signal that is indicative of the current flowing through thebranch circuit. Thus, for example, if the servers being supplied by thebranch circuit consume between a low of about 6 amps and a high of about10 amps (e.g., during peak usage of the hosted website) at 120 VAC, thenthe CT current sensor 203 will produce a scaled AC voltage indicative of6 to 10 amps (e.g., according to the turns ratio of the CT currentsensor to the part the CT current sensor is coupled to).

In this implementation, the CT current sensors 203 generate an inducedcurrent proportional to the actual current passing through a branchcircuit conductor that is installed through the air gap core of the CTcurrent sensor 203. The CT current sensors 203, for example, maycomprise a split-core or solid core device. A split-core CT currentsensor 203, for example, allows the CT core to open and enclose theconductor without disconnecting or de-energizing the circuit. A solidcore CT current sensor 203 may be used on a new installation before thecircuits are energized. As shown in FIGS. 2A and 2B, a plurality of CTcurrent sensors 203 (e.g., eight (8) in one implementation), connect toa collection device circuit board, also known as the CT interface (CTIF)board collection device 202. A plurality of CTIF boards collectiondevices 202 connect to the panel processor 101 (e.g., via Cat 5 cablesor other methods) as previously described to give a total circuitcapacity (e.g., a total capacity of at least 42 circuits in oneimplementation). One implementation supports six (6) CTIF boardcollection devices 202, although other implementations are possible. Inone implementation, each CTIF board collection device 202 provides asignal termination resistor for each of the connected CT currentsensors, converting the induced current that is proportional to thebranch circuit current into a voltage by Ohm's Law. In otherimplementations, for example, a digital signal (e.g., digital word)representing the sampled current value may be generated. In stillanother implementation, a branch circuit current may be indirectly ordirectly coupled with a Hall Effect sensor to generate an AC or DCvoltage proportional to the current in the conductor (as a function oftime), or further converted to a DC signal through a rectifier or othersignal conditioning circuit (e.g. integrator). Other implementations ofproviding a signal representative of a sampled current in a branchcircuit may also be used.

These voltages (or other signal indicative of the current level sensedin a branch circuit) are then routed to a single RMS-to-DC converterintegrated circuit 204 by means of a multiplexer integrated circuit 205under the control of a panel processor, such as by way of address selectlines 207. In one implementation, an 8:1 multiplexer and thus three (3)address select lines 207 are used, although other configurations arepossible. Other implementations, for example, could use a 16:1 or 32:1multiplexer for supporting more CT connections per CTIF 202. A benefitof using the RMS-to-DC converter circuitry 204 for the CT currentsensors 203 is that the installation of the CT sensors 203 becomesnon-critical since there is no longer a polarity associated with thecurrent value, easing installation. In another embodiment, the RMS-to-DCconverter 204 may be omitted for use with sensors other than CT sensors203 that product a DC voltage as their output, such as a Hall Effectcurrent sensor. The DC voltage produced by the RMS-to-DC convertercircuitry 204 (or directly from the multiplexer 205 in the case of a DCcurrent sensor implementation) is transmitted to an operationalamplifier circuit 206 provides buffering and a low-impedance output forthe CTIF board collection device 202 for transferring the DC voltagesignal to the panel processor. In an alternate implementation, theoperational amplifier circuit 206 could include non-inverting gain toincrease the amplitude of the DC voltage. The DC voltage output of theoperational amplifier 206 is connected to the signal output connector208 of the CTIF board collection device 202. The output signalradiometrically corresponds to a specific branch circuit current, andthe voltage is then sampled by the panel processor via an A/D converterand a periodic interval, nominally once per second (1 Hz), or at a ratesupported by the hardware and the customer's needs. In oneimplementation, the panel processor has a built-in A/D converter that ismultiplexed by the operating system to appear as individual A/Dconverter inputs (e.g., seven individual A/D converter inputs). Otherimplementations may employ external A/D converter devices, eithermultiplexed, or dedicated, per CTIF board collection device 202, or evenper CT sensor 203. The A/D converter, or A/D converters, may be part ofthe CTIF board collection device 202, or be part of the panel processor.In an alternate implementation, the CTIF board collection device 202 hasone or more A/D converters that transmit a CT digital word to the panelprocessor by a digital signal. In these implementations, the resultingdigital signal value is then stored in a panel processor memory forlater processing by software executing on the panel processor. The panelprocessor cycles through all the CTIF board collection devices 202 andattached CT sensors 203 connected to the CTIF board collection devices202 to represent all the digital branch circuit current values andstores the digital branch circuit current values in the panel processormemory.

FIG. 6 shows an example implementation of a system monitoring a branchcircuit 300. A collection of digital values representing the branchcircuit currents are interpreted by software executing on a panelprocessor as a current value, measured in Amperes RMS. In oneimplementation, for example, the panel processor executes twointerdependent programs that retrieve, process, and communicate thebranch circuit current values to the end user, or to another computer bymeans of a communications medium and protocol. In one embodiment, theprograms are written in server-side JavaScript, known as node.js. Otherprogramming languages such as, but not limited to, C, C++, or Python arepossible in alternate implementations. As shown in FIG. 6, the firstprogram, called the CT collection server (ctcServer) 301, interfaceswith the panel processor digital input and output (I/O) signals 303A andA/D converter inputs 303B to set the digital bits of the address linesconnected to the collection device's (e.g., a CTIF board collectiondevice's) multiplexers, and sample the voltage output of the collectiondevices, respectively. The ctcServer program uses control structures tosequence and sample the DC voltage outputs presented by the collectiondevices, and store the converted digital value in a distinct memorylocation 304 for each value. Upon completion of the collection,conversion, and storage of all the DC voltage values representing allthe branch circuit currents, then collates and transmits the digitalvalues to the second program via a network socket protocol 305, althoughany type of communication such as a generic communication channelbetween a physical and/or logical layer may be used. The second program,called the branch circuit monitor server (bcmServer) 306, receives thevalues from the ctcServer 301, stores them in distinct memory locations304, and computes short-term statistics 307 on the values for eachcircuit such as maximum, minimum, and average values, in addition to thecurrent real-time value of the branch circuit current. It also providesfor configuration of the panel processor via privileged access. In oneimplementation, the first and second programs execute on the same panelprocessor. In an alternate implementation, the two programs execute onseparate processors connected by a networking media and protocol, or byother physical and/or logical means.

The bcmServer 306 also instantiates and executes an embedded hypertexttransfer protocol (HTTP) server 308 to provide one or more networkedusers 309 with one of several visualizations of the branch circuitcurrent data 310. The HTTP server of the bcmServer 306 can communicatewith any number and type of HTTP clients such as, but not limited to,Internet Explorer, Firefox, or Google Chrome. The bcmServer 306 supportsalarm threshold that activate if a branch circuit current exceed a setvalue, or values, on an instantaneous, or time-averaged basis. ThebcmServer 306 will forward such alarm conditions to a central computer,or may display them on the embedded web server, or both. The bcmServer306 web server allows privileged users to configure elements of the BCMsuch as client/customer name associated with a circuit, change circuitbreaker amperage ratings, set, modify, and clear alarms, and performbuilt-in tests (BIT). The bcmServer 306 utilizes a configuration file311, such as in a JavaScript Object Notation (JSON) format, to store theparameters of each branch circuit such as customer name, circuit number,breaker capacity, CT number, etc. The configuration file can be modifiedthrough the privileged access or offline and uploaded to the panelprocessor. Alternate formats for the configuration file such as, but notlimited to, extensible markup language (XML) or comma separated values(CSV) are possible in alternative embodiments.

As shown in FIG. 7, in one implementation, the BCM devices' one or morepanel processor 400 communicate to a central computer 401 executingsoftware called the data center server (dcServer) 402. The centralcomputer 401, dcServer program 402, and two or more BCM devices comprisea BCM System (BCMS). The BCMS allows centralized access, data storage,querying, retrieval, and visualization of all the circuits in the datacenter. Additionally, through the central computer 401 and the dcServerprogram 402, the BCMS can communicate with third-party data centerinformation management (DCIM) or building management system (BMS)software 403 via standard or proprietary protocols as desired by thecustomer. Additionally, the central computer 401 and dcServer software402 may send alarm, status, or diagnostic messages to networked users bymeans SMS texts, email, or voice communications.

One useful feature of the BCMS is the storage, querying, and retrievalof historical branch circuit's current data. The central computer 401hosts a database management system (DBMS) 404 that stores and retrieveshistorical branch circuit current data. The DBMS 404 allows short-,medium-, and long-range data storage for each branch circuit. The panelprocessors 101 will send a running-average value of each branch circuitat a rate of once per minute ( 1/60 Hz) to the central computer thatstores each branch circuit value in the DBMS 404. In one implementation,the DBMS 404 will store these values in a circular buffer such that thelast 24 hours of 1/60 Hz data for each branch circuit current isavailable for viewing or analysis. Similarly, the DBMS 404 willcalculate and store running averages for the branch circuit currents atrates of once per quarter hour, hour, six hours, and daily in a similarcircular buffer of length commensurate with the sampling rate. Users canquery, view, and analyze branch circuit current data in graphical formatto look for trends or trouble conditions over a plurality of time anddate ranges.

As shown in FIG. 8, in an alternate embodiment, a BCMS supports branchcircuit current monitoring of DC currents. In this embodiment, thecurrent sensors comprise non-contact current sensors 501, such as usingHall Effect sensor devices 502 to produce a DC voltage that isproportional to the DC or AC current flowing through a branch circuitconductor. In one implementation for measuring only DC currents, forexample, the collection devices will bypass or omit the RMS-to-DCconverter circuitry 504 and directly connect the Hall Effect sensorvoltage through a multiplexer 505 to an operational amplifier circuit506. In one embodiment of the Hall Effect sensor 501, the branch circuitconductor is arranged parallel to the major plane of the Hall Effectsensor and the current is inferred by means of the Hall Effect. Melexisproduces Hall Effect current sensor integrated circuits that supportsuch an arrangement. In an alternate embodiment of the Hall Effectsensor, the branch circuit current induces a magnetic flux 508 in apermeable core 509 similar to that of a conventional CT, with the HallEffect sensor's main plane perpendicular to the flux flow. Severalmanufacturers produce Hall Effect sensors that support this arrangement.The software would be minimally changed to reflect a DC current versusan AC current.

As an alternate to the analog signal produced by the Hall Effect sensor,a variation of the aforementioned Hall Effect sensors outputs a digitalsignal, such as a pulse width modulation (PWM) waveform. This methodprovides increased accuracy and immunity to noise as compared to ananalog output. In place of an A/D converter, the panel processor startsa counter when the waveform transitions from low to high logic levels,and stops the counter when the waveform transitions from high to lowlogic levels. The counter value is compared to a value of the counterfor a high to high logic level interval, indicating a radiometricrepresentation of the current value.

In lieu of one or more current sensors connected to a collection device,one or more voltage sensors may be connected. A voltage sensor connectsbetween a phase voltage line and the neutral line of a polyphase system,typically two or three phases. The voltage sensor translates theline-to-neutral voltage down from a high voltage, typically 120V RMS toa lower voltage, typically less than 5V RMS. The voltage sensor outputthen connects to the collection device in a similar fashion as a currentsensor. The voltage is applied across the sensing resistor in the samemanner as the current sensor, and multiplexed and converted to a DCvoltage via the RMS-to-DC converter integrated circuit, or arectification circuit. The DC voltage is either transmitted to the panelprocessor and converted to a digital value by means of the panelprocessor A/D converter, or directly converted by means of an A/Dconverter resident on the collection device, and transmitted to thepanel processor as a digital signal to a digital input port on the panelprocessor.

The resulting digital values of the phase voltages are interpreted bythe software on the panel processor to represent Volts RMS. The phasevoltages are associated to one or more branch circuits by a definedpattern. Thus, for each branch circuit, a current sensor can determinethe branch circuit current measured in Amperes RMS, and the phasevoltage is determined by a voltage sensor voltage measured in Volts RMS.From these two values, the apparent power can be accurately calculatedmeasured in Volt-Amps (VA). The apparent power describes the accuratepower drawn by the branch circuit. In addition, energy usage by thebranch circuit can be calculated by integrating apparent power over atime interval. The resulting energy value is measured in Volt-Amp-hours(VA-h). This energy value can be used in subsequent calculations toestimate cooling requirements of a data center based on energy usage ofequipment connected to branch circuits.

The aforementioned Hall Effect sensors 501 may be calibrated to providehighly accurate readings. FIG. 9A depicts an example calibration setup.The method to calibrate one or more sensors involves using a goal-seekalgorithm and a test setup to provide a known value of current throughthe representative conductor that the sensor will be associated with bymeans of a calibration station. The response parameters of the DC sensorare an offset value and a full-scale reading value, both defined inAmperes. These two values are unique to each sensor and stored in theJSON configuration file 311 as described above. FIG. 9B gives analgorithm flowchart to accomplish the calibration for a sensor. Thealgorithm may be extended to allow calibration of any number of sensorsthat are connected to the calibration station. Once the calibration iscomplete, the new offset and full-scale values for each sensor arestored it the configuration file for use in an operational system. If asensor is replaced, or the conductor that it is measuring is changed,the calibration needs to be repeated with the new sensor and/or the newconductor.

Although embodiments of this invention have been described above with acertain degree of particularity, those skilled in the art could makenumerous alterations to the disclosed embodiments without departing fromthe spirit or scope of this invention. All directional references (e.g.,upper, lower, upward, downward, left, right, leftward, rightward, top,bottom, above, below, vertical, horizontal, clockwise, andcounterclockwise) are only used for identification purposes to aid thereader's understanding of the present invention, and do not createlimitations, particularly as to the position, orientation, or use of theinvention. Joinder references (e.g., attached, coupled, connected, andthe like) are to be construed broadly and may include intermediatemembers between a connection of elements and relative movement betweenelements. As such, joinder references do not necessarily infer that twoelements are directly connected and in fixed relation to each other. Itis intended that all matter contained in the above description or shownin the accompanying drawings shall be interpreted as illustrative onlyand not limiting. Changes in detail or structure may be made withoutdeparting from the spirit of the invention as defined in the appendedclaims.

What is claimed is:
 1. A branch circuit monitoring system, comprising: afirst collection device configured to receive direct current (DC)signals indicative of a measured DC current value from a first pluralityof current monitors and multiplex the DC signals from the firstplurality of current monitors; a second collection device configured toreceive DC signals indicative of a measured DC current value from asecond plurality of current monitors and multiplex the DC signals fromthe second plurality of current monitors; a panel processor device incommunication with the first and second collection devices configured toreceive the DC signals from each of the first and second currentmonitors, the panel processor device configured to store in a localmemory a plurality of data structures comprising the measured DC currentdata values.
 2. The branch circuit monitoring system of claim 1 furthercomprising a first plurality of current monitors, each of the firstplurality of current monitors comprising non-contact current sensorsconfigured to produce a DC voltage proportional to a DC current flowingthrough one of a first plurality of branch circuit conductors.
 3. Thebranch circuit monitoring system of claim 2 wherein the non-contactcurrent sensors of the first plurality of current monitors comprises atleast one Hall Effect sensor.
 4. The branch circuit monitoring system ofclaim 2 further comprising a second plurality of current monitors, eachof the second plurality of current monitors comprising non-contactcurrent sensors configured to produce a DC voltage proportional to a DCcurrent flowing through one of a second plurality of branch circuitconductors.
 5. The branch circuit monitoring system of claim 4 whereinthe non-contact current sensors of the first plurality of currentmonitors and the second plurality of current monitors each comprises atleast one Hall Effect sensor.
 6. The branch circuit monitoring system ofclaim 2 wherein at least two of the first plurality of current monitorsare each coupled with a sub-branch of a first branch circuit of thefirst plurality of branch circuits and configured to measure a currentvalue within the sub-branches of the first branch circuit of the firstplurality of branch circuits.
 7. The branch circuit monitoring system ofclaim 6 wherein a measured current value of the first branch circuit isdetermined by summing the measured current values of each of thesub-branches.
 8. The branch circuit monitoring system of claim 1 whereinthe panel processor polls the first and second collection devices forthe first and second DC signals.
 9. The branch circuit monitoring systemof claim 1 wherein the data structure comprises a branch identifier, ameasured current and a time stamp.
 10. The branch circuit monitoringsystem of claim 1 wherein the panel processor is configured to providethe data structure over a data connection to a building managementsystem.
 11. The branch monitoring system of claim 1 further comprising abuilding management system running on a server machine, the buildingmanagement system including a branch circuit monitoring moduleconfigured to receive the branch circuit monitoring data over a dataconnection, the branch circuit monitoring module further configured todisplay the branch circuit monitoring data within the buildingmanagement system.
 12. The branch monitoring system of claim 1 whereinthe signal indicative of the measured current comprises a voltage level.13. The branch monitoring system of claim 1 wherein the signalindicative of the measured current comprises a digital value.
 14. Thebranch circuit monitoring system of claim 1 wherein the panel processordevice comprises a network interface and is configured to communicatewith a server to provide the stored plurality of data structures via thenetwork interface.
 15. The branch circuit monitoring system of claim 14further comprising a server and an associated database configured toreceive data structures from the panel processors over a network via thenetwork interface of the panel processor device.
 16. The branch circuitmonitoring system of claim 1 wherein the first collection device isfurther configured to receive direct current (DC) signals indicative ofa measured DC voltage value from a first plurality of voltage monitors.17. The branch circuit monitoring system of claim 16 wherein the secondcollection device is further configured to receive direct current (DC)signals indicative of a measured DC voltage value from a secondplurality of voltage monitors.
 18. The branch circuit monitoring systemof claim 1 wherein the panel processor is configured for self-discoveryof a new collection device.
 19. A method of branch circuit monitoring,comprising: receiving, at a first collection device, a first pluralityof signals indicative of a first plurality of measured current values ofa first plurality of branch circuits; multiplexing, at the firstcollection device, the first plurality of signals indicative of thefirst plurality of measured current values; receiving, at a secondcollection device, a second plurality of signals indicative of a secondplurality of measured current values of a second plurality of branchcircuits; multiplexing, at the second collection device, the secondplurality of signals indicative of the second plurality of measuredcurrent values; receiving, at a panel processor in communication withthe first and second collection devices, the first and second pluralityof DC signals; and storing, in a local memory of the panel processor, aplurality of data structures comprising the measured branch circuitcurrent data values for said branch circuit along with a timestampassociated with a time at which the currents were measured.
 20. Themethod of claim 19 further comprising measuring a first plurality ofcurrents within a first plurality of branch circuits using a firstplurality of current monitors each coupled with a respective branch ofthe first plurality of branch circuits.
 21. The method of claim 20wherein the operation of measuring a first plurality of currents isperformed at least in part via at least one Hall Effect sensor.
 22. Themethod of claim 20 further comprising measuring a second plurality ofcurrents within a second plurality of branch circuits using a secondplurality of current monitors each coupled with a respective branch ofthe second plurality of branch circuits.
 23. The method of claim 22wherein the operation of measuring a second plurality of currents isperformed at least in part via at least one Hall Effect sensor.
 24. Amethod of calibrating the branch circuit monitoring system of claim 1,comprising: a calibration apparatus configured to deliver a knowncurrent through a conductor; and a calibration algorithm and software tosolve an equation representing the current sensor response to a currentthrough a conductor.